Method and structure for shoring a lateral face of an excavation



Nov. 24, 1970 Filed April 18, 1969 H. SCHNABEL, JR

METHOD AND STRUCTURE FOR SHORING A LATERAL FACE OF AN EXCAVATION 3 Sheets-Shed 1 INVENTOR HARRY SCHNABEL,JR

* ATToRNEYs Nov. 24, 1970 H. SCHNABEL, JR 3,541,798

METHOD AND STRUCTURE FOR SHORING A LATERAL FACE OF AN EXCAVATION Filed April 18, 1969 3 Sheets-Sheet 2 INVENTOR HARRY SCHNABEL,JR

ATTORNEYS Nov. 24, 1970 SCHNABELQJR 3,541,798

METHOD AND STRUCTURE FOR SHORING A LATERAL FACE OF AN EXCAVATION Filed April 18, 1969 3 Sheets-Sheet 3 INVENTOR HARRY SCHNABELJR Mm Wm ATTORNEYS United States Patent 3,541,798 METHOD AND STRUCTURE FOR SHORING A LATERAL FACE OF AN EXCAVATION Harry Schnabel, Jr., 5272 River Road, Bethesda, Md. 20015 Filed Apr. 18, 1969, Ser. No. 817,330 Int. Cl. E02d 5/08 US. C]. 6139 9 Claims ABSTRACT OF THE DISCLOSURE A method and structure for shoring a lateral face of an excavation which face is defined partially by an earthen overburden and partially by a rock underlayer and is supported by a sheeting wall of soldier beams and lagging members reinforced by tie back, with vertical support members smaller than the soldier beams connected to and extending downwardly from the bases of the beams and anchored in the rock underlayer to permit transfer of load to such members thereby preventing failure of the rock underpinning the wall.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to structures for shoring the lateral faces of excavations. Specifically, the invention concerns a structure for shoring the lateral face of an excavation, wherein the face is partially defined by an earthen overburden and partially defined by a rock underlayer.

Description of the prior art Structures for shoring the lateral faces of excavations are well-known and particularly for shoring such faces which are entirely defined by earthen material. Frequently, however, an excavation must be extended downwardly into a layer of rock underlying an earthen overburden, so that the lateral faces of such an excavation are partially defined by the overburden and partially defined by the underlayer. The portions of the lateral faces defined by the rock underlayer generally do not require shoring as do the earthen overburden portions of such faces. Usually, therefore, sheeting walls are installed along the overburden portions of the faces with the bases of the walls abutting the upper surface of the underlayer.

A structure of this type of illustrated in White Pat. 3,226,933, and includes a plurality of vertically extending soldier beams which are horizontally spaced apart along the overburden portion of a lateral face of an excavation. A plurality of lagging members are associated with the soldier beams and bear against the overburden portion of the face. To counteract the inwardly directed force applied to the sheeting wall by the overburden, a plurality of downwardly and outwardly extending tie-backs are secured between the wall and the underlayer, and placed under tension. The tie-backs thus apply a downwardly and outwardly directed force to the wall, the outwardly directed component of which opposes the inwardly directed force applied to the wall by the overburden. The downwardly directed component of the force applied to the wall by the tie-backs is transmitted into the underlayer through the bases of the soldier beams.

After the sheeting wall and tie-backs have been installed, the excavation is extended downwardly into the underlayer, resulting in the removal of rock a short distance inwardly from the base of the wall and thus forming a rock shelf. The bases of the soldier beams abut the upper surface of the underlayer a short distance outwardly from the edge of this shelf. The downwardly directed 3,541,798 Patented Nov. 24, 1970 component of the force applied to the wall by the tiebacks is thus supported by a relatively narrow column of rock underpinning each soldier beam. This loading condition frequently causes such underpinning rock columns to fracture sufficiently to cause rock to spall away from the portion of the face defined by the underlayer and fall into the excavation, thus destroying the underpinnings for the soldier beams. Obviously such an occurrence is not only dangerous to personnel and equipment, but necessitates time-consuming and expensive repairs to re-establish such underpinnings.

One possible method of obviating this problem would be to insert the soldier beams into the underlayer so that the bases thereof are positioned below the upper surface of the layer. However, in order to insert the beams into the underlayer, holes would have to be drilled therein for accommodating the beams, and due to the size of the holes that would be required for accommodating conventional soldier beams such a procedure would be prohibitively expensive.

SUMMARY OF THE INVENTION The present invention offers an economical solution to the problem of spalling associated with the prior art methods and structures for shoring the lateral faces of excavations.

The structure of the invention is adapted to be used for shoring the lateral face of an excavation, wherein the face is partially defined by an earthen overburden and partilly defined by a rock underlayer, and generally comprises; a sheeting wall bearing against the portion of the lateral face defined by the overburden and including at least one substantially vertically extending soldier beam having the base thereof abutting the underlayer; at least one tie-back extending downwardly and outwardly from the wall through the overburden into the underlayer and being secured at one end to the wall and anchored at the other end in the underlayer, the tie-back being tensioned for applying a downwardly and outwardly directed force to the wall, the outwardly directed component of the force applied to the wall by the tie-back opposing the inwardly directed force applied to the wall by the overburden; and at least one support member extending downwardly from the base of the soldier beam into the underlayer and being secured at one end to the base of the soldier beam and anchored at the other end in the underlayer so that downwardly directed force applied to the wall by the tieback may be borne by the support member to deter the rock from spalling away from the portion of the lateral face defined by the underlayer, the area of the smallest circle which will enclose the cross-section of the support member being substantially less than the area of the smallest circle which will enclose the cross-section of the soldier beam.

The method of the invention is adapted to be employed for shoring a lateral face of an excavation, said face being partially defined by an earthen overburden and partially defined by a rock underlayer, the portion of the face defined by said overburden being laterally supported by a sheeting wall bearing thereagainst and including at least one substantially vertically extending soldier beam having the base thereof abutting said underlayer, and at least one tie-back extending downwardly and outwardly from said wall through the overburden into the underlayer and being secured at one end of the wall and anchored at the other end in the underlayer, said tie-back being tensioned for applying a downwardly and outwardly directed force to the wall, the outwardly directed force applied to the wall by the tie-back opposing the inwardly directed force applied to the wall by the overburden, and basically comprises; forming adjacent the base of the soldier beam a 3 hole extending downwardly into the underlayer and having a cross-sectional area substantially less than the smallest circle which would enclose the cross-section of the soldier beam; inserting an elongated support member downwardly into said hole; anchoring one end of the support member in the underlayer; and securing the other end of the support member to the base of the soldier beam so that downwardly directed force applied to the wall by the tie-back may be 'borne by the support member to deter rock from spalling away from the portion of the lateral face defined by the underlayer.

Preferably, the sheeting wall is a conventional sheeting wall comprising a plurality of vertically extending soldier beams and a plurality of lagging members associated with the beams. Also, preferably, a plurality of conventional tie-backs are employed.

One of the support members preferably is secured to the base of each soldier beam. The support members will thus support the downwardly directed component of the force applied to the wall by the tie-backs should the rock columns underpinning the soldier beams begin to fracture.

Preferably, the support members comprise highstrength metallic rods which are anchored in the rock layer, and are most effectively used by extending the members downwardly from the bases of the soldier beams into the rock underlayer beneath the level of the bottom of the excavation.

Also, if desired, and as a further deterrent to spalling, wale members may be secured across the portion of the lateral face of the excavation defined by the underlayer.

With the foregoing in mind, it is an object of the present invention to provide an improved method and structure for shoring the lateral face of an excavation which face is partially defined by an earthen overburden and partially defined by a rock underlayer underlying the overburden.

It is also an object of the invention to provide a method and structure as described in the preceding object in which tie-backs are used for applying a downwardly and outwardly directed force to a sheeting wall bearing against the portion of the lateral face defined by the overburden and in which means other than the rock underpinning the wall, are provided for assuming support of the downwardly directed component of such force, to thereby prevent spalling of the rock.

It is a further object of the invention to provide a method and structure as described in the preceding object in which the support assuming means comprise support members extending downwardly from the base of the sheeting wall into the underlayer.

It is an additional object of the invention to provide a method and structure as described in the preceding object in which the support members are capable of assuming support of the entire downwardly directed component of the force applied to the sheeting wall by the tie-backs and are economical to install.

These and other objects of the invention will become apparent upon a consideration of the detailed description of a preferred embodiment thereof given in connection with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view through the lateral face of an excavation, showing the structure of the invention;

FIG. 2 is a front vew of the structure shown in FIG. 1;

FIG. 3 is a sectional view taken on line 3-3 of FIG. 1;

FIG. 4 is a side view of a portion of the structure of the invention;

FIG. 5 is a sectional view similar to FIG. 1, showing an optional structural feature that may be employed with the structure of the invention; and

FIG. 6 is a front view of the structure shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Frequently the excavation for a building foundation or the like must be extended downwardly into a rock underlayer underlying an earthen overburden. Such an excavation is shown in FIG. 1, wherein an excavation 10 extends downwardly into an underlayer of rock 12 underlying an earthen overburden 14. Excavation 10 has a lateral face 16 which is partially defined by the earthen material comprising overburden 14 and partially defined by the rock comprising underlayer 12.

Usually the interface between overburden 14 and underlayer 12 is neither compositionally nor geometrically as well defined as is shown in the drawings. An abrupt planar dichotomy between the overburden and underlayer has been shown in the drawings for the purpose of avoiding the showing of geological details which are unnecessary to an understanding of the invention.

Rock underlayer 12 is composed of a relatively hard material which is substantially self-supporting, such as granite or limestone. Therefore, generally no external means are required for shoring the portion of face 16 defined by underlayer 12. Overburden 14, however, is composed of relatively discrete earthen particles which are not self-supporting; the term earthen as used herein being intended to mean all types of earthen material such as clay, sand, humus, mixtures of such materials, and mixtures of such materials and particles of rock. Therefore, external means, such as a sheeting wall 20, are required for shoring the portion of face 16 defined by overburden 14.

Sheeting wall 20 includes a plurality of vertically extending, horizontally spaced soldier beams 22 (FIGS. 1 and 2). Prior to the removal of any substantial amount of earthen material from excavation 10, soldier beams 22 are driven to refusal against the upper surface of underlayer 12. A plurality of lagging members 24 (FIGS. 1 and 2) are then associated with soldier beams 22 as earthen material is removed from the excavation. Conveniently soldier beams 22 are H-beams permitting lagging members 24 to be easily positioned between the flanges of the beams. Alternatively, the lagging members may be longer than the spacing between adjacent soldier beams and secured to the outer faces of the inner flanges of the beams, i.e., the flange faces nearest excavation 10, by suitable connectors.

Means are provided for applying an outwardly directed force to wall 20 to counteract the inwardly directed force applied to the wall by overburden 14. Such means comprise a plurality of tie-backs 26 and 28 (FIG. 1), which extend downwardly and outwardly from wall 20 through overburden 14 into underlayer 12. Each tie-back is secured at one end to wall 20 and anchored at the other end in underlayer 12. The number and location of tiebacks 26 are determined by the magnitude of the outwardly directed force required. Tie-backs 26 are installed after the bottom of the excavation adjacent wall 20 has reached the level at which the tie-backs are to be secured to the wall. Tie-backs 28 are installed and secured to wall 20 near the base thereof after the bottom of the excavation adjacent the wall has reached the upper surface of underlayer 12.

The tie-backs each include a tendon 34 which extends outwardly and downwardly from wall 20 through over burden 14 into underlayer 12. Any conventional process, such as drilling, may be used for positioning tendons 34. The outer end of each tendon is anchored in underlayer 12 by a suitable anchoring means, such as by grouting 36.

Pluralities of wale members 30 and 32 are provided for securing tendons 34 to wall 20. The wale members are horizontally disposed across the outer faces of the inner flanges of soldier beams 22 and connected thereto, as by welding.

After the outer ends of tendons 34 have anchored in underlayer 12, the inner ends of the tendons are attached to wale members 30 and 32 by suitable connectors 38. The tendons are then placed under tension for applying a downwardly and outwardly directed force to wall 20; the magnitude of the outwardly directed component of which is sufficient to counteract the inwardly directed force ap plied to the wall by overburden 14.

The structure described above, including sheeting wall 20 and tie-backs 26 and 28, is a conventional structure for shoring the lateral face of an excavation.

As will be apparent, the downwardly and outwardly directed force applied to wall 20 by tie-backs 26 and 28 also includes a downwardly directed component, which in the absence of other means, is transmitted into underlayer 12 through the bases of soldier beams 22. After wall 20 and tie-backs 26 and 28 have been installed, excavation is extended downwardly into underlayer 12 forming a rock shelf. The bases of solder beams 22 abut this shelf near the edge thereof so that the downwardly directed component of the force applied to wall by tie-backs 26 and 28 is supported by a relatively narrow column of rock underpinning each soldier beam.

Generally, the outwardly directed component of the force applied to wall 20 by tie-backs 26 and 28 must be of a substantial magnitude in order to effectively oppose the inwardly directed force applied to the wall by overburden 14. Thus, the downwardly directed component of the force applied to the wall by the tie-backs is also usually of a substantial magnitude, frequently being as great as 200,000 lbs. at the base of each soldier beam, and imposes severe compression loads on the rock columns underpinning the soldier beams. As a result of this loading condition, the underpinning rock columns frequently fracture sufiiciently to cause rock to spall away from face 16 and fall into excavation 10, thus destroying the underpinnings for the soldier beams and permitting the beams to slide downwardly. Obviously such an occurrence presents a hazard to both the personnel and equipment within the excavation and necessitates time-consuming and expensive repair procedures to reestablish sound underpinnings for the soldier beams.

The structure of the invention is designed to obviate the foregoing problem and includes means other than the rock columns underpinning soldier beams 22 for assuming support of the downwardly directed component of the force applied to wall 20 by tie-backs 26 and 28. Such means comprise a plurality of support members extending downwardly from the base of wall 20 into underlayer 12, and preferably into the underlayer beneath the level of the bottom of excavation 10.

Conveniently the support members comprise high strength metallic rods 40 (FIGS. 14), such as steel reinforcing rods of the type employed in reinforcing concrete. Each of the rods is secured to the base of one of the soldier beams by a relatively short T-beam section 42, with the upper end of each rod "40 being welded to the central flange of a section 42 and the peripheral flange of the section being welded to the outer face of the inner flange of one of the soldier beams.

Holes 46 are formed in layer 12 slightly inwardly from the bases of soldier beams 22, by any conventional process, such as by drilling, for accommodating rods 40. The rods are anchored in holes 46 by any convenient means, such as by grouting 47. Rods 40 may be installed either before or after tie-backs 28 have been installed.

The downwardly directed force component may progressively fragment the rock columns underpinning the soldier beams, particularly at the upper ends thereof, and if such fragmentation is permitted to continue unchecked, the columns could become sufficiently fractured to cause rock to spall away from the portion of face 16 defined by underlayer 12. However, when rods 40 are installed, the downwardly directed force component is transferred progressively from the rock columns to the rods as the column fragment to any small degree and thus begin to yield. The rods preferably are designed to bear 100% of the force component with a reasonable safety factor. Thus, before the rock columns have fractured sufiiciently to cause rock to spall away from the portion of face 16 defined by layer 12, all of the downwardly directed force component will 6 have been transferred to rods 40; the latter thereafter acting as columns to transmit the force component into underlayer 12, preferably beneath the level of the bottom of excavation 10. As will be apparent, the quantity of rock underpinning the bases of rods 40 beneath the level of the excavation bottom is suflicient to support the force component transmitted through the rods without fragmenting. In this manner the integrity of the portion of face 16 defined by underlayer 12 is maintained, thus maintaining sound underpinnings for the soldier beams.

Moreover, the area of the smallest circle which willenclose the transverse cross-section of one of rods 40, and thus the cross-sectional area of each of the holes 46, is substantially less than the area of the smallest circle which will enclose the transverse cross-section of one of soldier beams 22, i.e., the area of a circle generated by rotating a line which extends from the geometric center of the transverse cross-section of one of rods 40 to a point on the periphery of the cross-section furthest form the geometric center, about the longitudinal axis of the rod which passes through the geometric center, is substantially less than the corresponding area of one of the soldier beams. Thus, although the soldier beams themselves might be inserted into the underlayer for accomplishing the function of rods 40, the expense of drilling holes therein large enough to accommodate the beams would be prohibitive. The substantially smaller holes 46, however, within which rods 40 are accommodated may be formed in layer 12 at a reasonable expense.

As described above, tie-backs 28 are secured to wall 20 near the base thereof. This arrangement insures that the base of the wall will not slide inwardly toward the edge of the rock shelf formed in underlayer.

If desired, and as a further deterrent to spalling, a plurality of wale members 58 (FIGS. 5 and 6) may be secured to the portion of lateral face 16 defined by the underlayer. Wale members 48, only one of which is shown in the drawings, are horizontally disposed along face 16, and are secured thereto by rock ties 50. The rock ties are structurally similar to tie-backs 26 and 28 including tendons 52 which are anchored in underlayer 12 by a suitable anchoring means, such as by grouting 54.

Preferably, wale members 48 are formed in relatively short sections, the medial portion of each of which is aligned with one of rods 40, with a rock tie 50 being disposed at each end thereof for securing the wale member to face 16. Tendons 52 need not be placed under as great a tension as are tendons 34 of tie-backs 26 and 28, since the portion of face 16 defined by underlayer 12 is essentially self-supporting.

The desirability of employing wale members 48 is determined by several factors including, the composition of underlayer 12, the magnitude of the downwardly directed force component, and the depth to which excavation 10 extends below the upper surface of the underlayer.

The method of the invention will be apparent from the foregoing description of the structure thereof, and includes forming holes 46 in underlayer 12 adjacent the bases of soldier beams 22, after wall 20 and tie-backs 26 have been installed and either before or after tie-backs 28 have been installed. Rods 40 are then inserted into holes 46 and one end of each rod is anchored in underlayer 12. The other end of each rod is thereafter secured to the base of one of the soldier beams so that the downwardly directed force component will be transferred to the rods from the rock columns underpinning the soldier beams before the columns have fractured sufficiently to cause rock to spall away from the portion of face 16 defined by underlayer 12.

Although the foregoing constitutes a detailed description of a preferred embodiment of the invention, it is recognized that various modifications thereof will occur to those skilled in the art. For example, means other than T- beam sections might be used for securing the support members to the bases of the soldier beams. Therefore, the

scope of the invention is to be limited solely by the scope of the claims appended hereto.

I claim:

1. A structure for shoring the lateral face of an excavation said face being partially defined by an earthen overburden and partially defined by a rock underlayer underlying said overburden, said structure comprising:

a sheeting wall bearing against the portion of the lateral face defined by said overburden, and including at least one substantially vertically extending soldier beam having the base thereof abutting said underlayer;

at least one tie-back extending downwardly and outwardly from said wall through the overburden into the underlayer and being secured at one end to the wall and anchored at the other end in the underlayer, said tie-back being tensioned for applying a downwardly and outwardly directed force to the wall, the outwardly directed component of the force applied to the wall by the tie-back opposing the inwardly directed force applied to the wall by the overburden; and

at least one support member extending downwardly from the base of the soldier beam into the underlayer and being secured at one end to the soldier beam and anchored at the other end in the underlayer so that downwardly directed force applied to the wall by the tie-back may be borne by said support member to deter the'rock from spalling away from the portion of the face defined by the underlayer, the area of the smallest circle which would enclose the cross-section of the support member being substantially less than the area of the smallest circle which would enclose the cross-section of the soldier beam.

2. A structure as recited in claim 1; wherein said sheeting wall comprises a plurality of said soldier beams horizontally spaced apart along the lateral face and a plurality of generally horizontally extending lagging members associated with the beams; and including a plurality of said support members, each of said support members being secured to the base of one of said beams.

3. A structure as recited in claim 1; further comprising at least one Wale member secured to the portion of the lateral face defined by the underlayer to further deter rock from spalling away from the portion of the face defined by the underlayer.

4. A structure as recited in claim 3; wherein said wale member is secured to the lateral face by at least one rock tie extending from the Wale member into the underlayer and being secured at one end to the wale member and anchored at the other end in the underlayer.

5. A structure as recited in claim 1; including a plurality of said tie-backs, one of which is secured to the lower portion of the sheeting wall to prevent the base of the wall from sliding inwardly.

6. A structure as recited in claim 1; wherein said support member extends downwardly into the underlayer beneath the level of the bottom of the excavation.

7. A structure as recited in claim 1; wherein the upper end of said support member is spaced inwardly from the base of said soldier beam; and further comprising a connecting member interposed between and fixedly attached to said support member upper end and said soldier beam base.

8. A method for shoring a lateral face of an excavation, said face being partially defined by an earthen overburden and partially defined by a rock underlayer underlying said overburden, the portion of the face defined by said overburden being laterally supported by a sheeting wall bearing thereagainst and including at least one substantially vertically extending soldier beam having the base thereof abutting said underlayer, and at least one tie-back extending downwardly and outwardly from said Wall through the overburden into the underlayer and being secured at one end to the wall and anchored at the other end in the underlayer, said tie-back being tensioned for applying a downwardly and outwardly directed force to the wall, the outwardly directed force applied to the wall by the tie-back opposing the inwardly directed force applied to the Wall by the overburden, said method comprising:

forming adjacent the base of said soldier beam a hole extending downwardly into the underlayer and having a cross-sectional area substantially smaller than the smallest circle which would enclose the crosssection of the soldier beam;

inserting an elongated support member downwardly into said hole;

anchoring one end of said support member in the underlayer; and

securing the other end of said support member to the base of the soldier beam so that downwardly directed force applied to the wall by the tie-back may be borne by the support member to deter the rock from spalling away from the portion of the lateral face defined by the underlayer.

9. A method as recited in claim 8, wherein said hole is formed and said support member is inserted downwardly into the underlayer beneath the level of the bottom of the excavation.

References Cited UNITED STATES PATENTS 3,226,933 1/1966 White 61-39 3,243,963 4/1966 Schnabel 61-39 3,371,494 3/1968 Lagerstrom 61--39 DAVID J. WILLIAMOWSKY, Primary Examiner P. C. KANNAN, Assistant Examiner U.S. Cl. X.R. 52-169; 61-50 

